If a password database is found in the persistent volume, a dialog
appears and asks for the passphrase to unlock that password database.
Enter the passphrase and click OK.

If you enter an invalid passphrase the following error message
appears:

The following error occured while opening the
database:
Hash test failed.
The key is wrong or the file is damaged.

Then click OK and try again.

KeePassX user guide

To read the official KeePassX user
guide, choose
Help ▸
KeePassX Handbook….

Use KeePassX to type a password into Pinentry

When using OpenPGP with Claws Mail or OpenPGP
Applet for example, you need to enter a password in a Pinentry dialog box. But you cannot copy and
paste into it. This is a security feature of Pinentry based on the fact that otherwise the
data in the clipboard could be accessed by another application against
your will.

Use the AutoType feature of KeePassX to type a password into a Pinentry dialog box.